Gauff has not appeared confident with her serve since beating Aryna Sabalenka on clay earlier this summer. She won three matches in the US Open tuneup earlier at the Cincinnati Open, but lost to Italy's Jasmine Paolini in the fourth round. Last week in Cincinnati, Gauff said she's practicing patience on tour the rest of the season.

Coco Gauff has not made a formal announcement, but a source confirmed to ESPN on Wednesday that the world No. 3 player has fired coach Matthew Daly and brought in Gavin MacMillan.

Prior to the start of the U.S. Open, Coco Gauff announces the firing of both her coaches amid a recent string of loses.